Amongst refractive surgical techniques (surgery of the cornea) seeking to correct ametropia, one of the known techniques is derived from the technique developed by Jose Barraquer and known as in situ keratomileusis. It consists in slicing a disk from the cornea by means of a microkeratome. The disk is raised, after which a small lens is removed from the plane uncovered by raising the disk, where the thickness and the dimensions of the small lens are a function of the correction to be provided. Thereafter, the disk of cornea is replaced on the plane that has been modified in this way, thus giving rise to a modification to the front surface of the cornea, and hence modifying its optical characteristics.
Interest in that technique has recently been renewed by use of the excimer laser which makes it possible to remove tissue extremely precisely. This has made it possible to control the dimensions of the small lenses in very much finer manner than with the previously used mechanical means.
In this type of surgery, the disk is removed by means of a microkeratome, i.e. a tool that is similar to a miniature plane having a blade that vibrates in the direction of its cutting edge, and the depth of cut is adjusted by means of wedges of precalibrated thickness or by micrometer screws.
All of the appliances available on the market comprise two parts:
a base ring of the appliance which is pressed against the eye around the cornea by an annular suction chamber; and PA1 a carriage carrying the blade and driven either by hand or automatically in slideways provided at the top portion of the fixing ring. PA1 a base comprising an annular suction chamber having an axis of symmetry, shaped to be pressed around the cornea of an eye, and provided with means for connection to a vacuum source; PA1 a cornea-shaping element situated above the base and having a surface facing it; and PA1 a cutting blade displaceable in a plane situated between the surface of the shaping element and the base.
The opportunities for setting and adjusting those devices are rather few or they require additional parts. To adjust the thickness of the cornea disk, the distance between the cutting edge of the blade and a plate situated in front of the edge of the blade is adjusted. The plate serves to flatten the cornea before the blade acts on it. To act on the diameter of the disk to be sliced off, it is generally necessary to have a set of fixing rings of different sizes.
In addition, certain appliances provide a keratome with a vibrating blade which moves on its own between the ring and the cornea flattening plate. Other appliances propose a keratome in which the blade, which is inclined relative to the plane of cut, moves together with the cornea flattening plate. Under such circumstances, it is appropriate to insert and move the carriage carrying the cutting blade in guiding slideways of the ring, but that operation is difficult, awkward, and not ergonomic.